A 4-year-old boy has recurrent urinary tract infections and a poor urinary stream. Voiding cystourethrogram shows a dilated posterior urethra, a small-calibre anterior urethra, trabeculated thick-walled bladder, and bilateral vesicoureteric reflux. What is the MOST likely diagnosis?
- A Ureteropelvic junction obstruction
- B Posterior urethral valves ✓
- C Vesicoureteric junction obstruction
- D Neurogenic bladder
Correct answer: B. Posterior urethral valves
Explanation
Posterior urethral valves are the commonest cause of lower urinary tract obstruction in boys. The voiding cystourethrogram shows dilation of the posterior urethra proximal to the valve with a sharp calibre change to the normal anterior urethra, plus secondary changes of trabeculation, diverticula, and reflux. Ureteropelvic and vesicoureteric junction obstructions cause upper tract dilation without urethral abnormality. Neurogenic bladder shows trabeculation but a normal urethral calibre transition.
Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.
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